DORSET scientists have helped to solve a butterfly mystery which had left conservationists in a flap.

In one of the largest citizen science projects ever undertaken, researchers from Butterfly Conservation in Lulworth helped to work out the travelling patterns of common migrant butterfly, the painted lady.

The butterfly arrives on UK shores from Africa each summer.

Up until now, it was unknown if it made the return journey or died on UK shores.

But after more than 60,000 public sightings across Europe were collected in 2009, the results are in – and they show that the painted lady does make the return journey.

Except this is done in several stages, meaning the butterflies that arrive back in Africa are several generations removed from those that set off.

Richard Fox, surveys manager at Butterfly Conservation, said: “The extent of the annual journey undertaken by the painted lady butterfly is astonishing.

“This tiny creature weighing less than a gram with a brain the size of a pinhead and no opportunity to learn from older, experienced individuals, undertakes an epic intercontinental migration in order to find plants for its caterpillars to eat.

“Once thought to be blindly led, at the mercy of the wind, into an evolutionary dead end in the lethal British winter, this amazing combination of mass-participation citizen science and cutting-edge technology has shown painted ladies to be sophisticated travellers.”

Radar records revealed that painted ladies fly at an average altitude of more than 500 metres on their southbound trip and can clock up speeds of 30mph.

The findings also revealed that the species undertakes a phenomenal 9,000-mile round trip from tropical Africa to the Arctic Circle – almost double the length of the famous migrations undertaken by monarch butterflies in North America.

Radar in Hampshire operated by Rothamsted Research revealed that around 11 million high-flying painted ladies entered the UK in spring 2009 with 26 million departing in autumn.

Dr Jason Chapman, a researcher at Rothamsted Research, said: “The apparent lack of a return migration of the late-summer generation of painted lady butterflies was one of the greatest enigmas in insect migration ecology.

“But, through a combination of traditional monitoring by butterfly enthusiasts and new radar techniques, we have finally solved this long-standing puzzle. Migrant insects continue to amaze the public and research community.”